1. Field of the Invention
The invention relates to an aqueous cosmetic antiperspirant formulation with increased antiperspirant effectiveness.
For aesthetic reasons in particular, transparent and translucent products are preferred by many consumers. Thus, transparent formulations are often used, for example, as deodorant or antiperspirant (AP). These can nowadays be realized by the following technologies:                1. aqueous-alcoholic formulations        2. water-in-silicone emulsions        3. microemulsions        
The aqueous-alcoholic deodorant and AP formulations are mostly based on water and alcohol as medium, deodorant and antiperspirant agents as active ingredients, and also perfume, solubilizers and thickeners (mostly based on carbohydrate) as additional agents. They are perceived by the consumer as being fresh and cooling, but are at the same time encumbered with a whole series of disadvantages. Thus, for example, application primarily to freshly shaved skin is associated with incompatibilities as a result of the alcohol content. Another major disadvantage is the fact that relatively large amounts of oil cannot be incorporated into such systems. As a result of the high content of antiperspirant salt required for highly effective performance, a white residue remains following application to the skin; this is perceived by the consumer as being extremely troublesome. However, due to the absence of a sufficiently large oil phase for technical reasons, this cannot be concealed. Moreover, the use of carbohydrate thickeners leads to high stickiness of the product after the alcohol has evaporated.
Water-in-silicone emulsions belong to the group of water-in-oil emulsions. The water phase comprising ethanol or polyhydric alcohols, such as, for example, propylene glycol and water-soluble active ingredients, such as AP agent and/or deodorant active ingredient, constitutes about 75-90% of the formulation. The oil phase consists of a volatile and a nonvolatile silicone oil and also a silicone emulsifier.
2. Discussion of Background Information
The transparency of water-in-silicone emulsions is based on matching the refractive indices of the two phases. It is a drawback that even a difference in the indices of 0.0004 caused, for example, by evaporation, leads to cloudiness. WO 98/32418 and WO 92/05767 describe such deodorant or AP formulations based on W/Si emulsion.
One approach for solving the described disadvantages has been made possible through cosmetically pleasing alcohol-free and transparent products which are based on so-called microemulsions. These have the major advantage that even relatively large amounts of various oils—with all of the described positive effects for the consumer—can be stably incorporated. Formulations of this type are in principle available by means of phase inversion temperature technology (PIT) or high-pressure homogenization. The required stability of the emulsifier system to high concentrations of antiperspirant salts, however, places high demands on the formulation skill of the product developer.
WO 98/15255 describes microemulsions. However, a drawback even with these formulations is a sticky feel on the skin caused by the thickener, and the lack of a yield point.
It is an object of the present invention to provide a cosmetic preparation which enriches the prior art and helps to avoid its disadvantages.
In particular, it is the object of the present invention to provide a cosmetic formulation which is transparent and is characterized by minimized stickiness. In particular, the object was to provide an antiperspirant formulation which is transparent and has no cloudiness at all, which is characterized by a minimized stickiness and which has a defined yield point for optimized discharge and application.
To increase the antiperspirant effectiveness, it is customary to increase the amount of antiperspirant active ingredient, such as, for example, aluminum chlorohydrates ACH. Furthermore, so-called activated aluminum chlorohydrates (AACH) are known as antiperspirant active ingredients with increased effectiveness, e.g. EP 925783 or in the literature—Antiperspirants and Deodorants, 2nd Edition, Cosmetic and Technology Science, Vol. 20, 1999.
However, it is a problem here that the antiperspirant effectiveness is only possible to a limited degree through increasing the amount of active ingredient since, above a content of about 15% by weight of the AP active ingredient, saturation of the effectiveness is established and in addition disadvantages such as white residues and an unpleasant feel on the skin are increased.
A few chemical basics in this regard:
If aluminum salt AlX3 of a strong acid (e.g. AlCl3) is dissolved in water, then, in accordance with the reaction:AlX3+6H2O→Al(H2O)63++3X−the octahedrally constructed hexaaquaaluminum ion [Al(H2O)6]3+ is formed, which acts as a weak cationic acid.
As a consequence of the acid effect, these are liable to hydrolysis and can be successively deprotonated as far as the hexahydroxoaluminate ion [Al(OH)6]3+.
Depending on the pH and the concentration of aluminum ions, three-dimensional structures are formed as a result of bridging with hydroxide ions and oxygen atoms. These processes, in which element atoms are bridged by hydroxide ions, are called olation and for bridges with oxide ions, the term used is oxolations.
Both reactions belong to the group of condensation reactions.
The polynuclear aluminum cations [Alm(OH)n(H2O)o]p+ present in aqueous aluminum salt solutions belong to the group of isopolyoxo cations.
In order to achieve an increased antiperspirant effectiveness of classic aluminum chlorohydrate (ACH) solutions, these are thermally treated depending on concentration, temperature and pressure, and the resulting solutions are dried by means of spray-drying.
This leads to an increased amount of smaller molecule sizes being present in stable form. However, these activated aluminum complex salts (AACH) effective as antiperspirant disintegrate in water back to their original equilibrium state, meaning that in aqueous preparations increased effectiveness is lost.
Use of these activated ACH types (AACH) has therefore hitherto only made sense in nonaqueous systems since otherwise reconversion to the molecule size distribution as occurs in classic ACH solutions is possible, as described, for example, in the article by A. H. Rosenberg—Antitranspirant Technology, SÖFW-Journal, 128 (4) 2000.
It is therefore an object of the present invention to provide an aqueous preparation which has an increased antiperspirant effectiveness without the described disadvantages. In particular, it is therefore the object to provide aqueous cosmetic preparations which, despite the water content, have an increased antiperspirant effectiveness as a result of the addition of activated aluminum complex salts.